The present invention relates to an explosive cartridge used in blasting operations for boring of tunnels, construction of roads, minings, quarryings, etc., and a paper polyethylene-laminated in both the sides thereof used for the explosive cartridge.
The explosives used for blasting are usually offered as cartridges. In a case of dynamite or powdery explosives, for instance, a fixed amount of explosive is packaged with paper to form a cartridge. In the case of water-bearing explosives, the explosive is packaged with a single- or double-ply tubular sheet made of a plastic such as polyethylene, nylon or polypropylene, and the packed tubular sheet is closed at both ends with metal clips (this type of cartridge being hereinafter referred to as "polyfilm cartridge"), or the explosive is packaged with paper or polyethylene-laminated paper, i.e., paper having its one side or both sides laminated with polyethylene.
However, polyfilm cartridge is recently not preferred by users since the explosive cartridges are prone to over-ride or to have foreign substances between them when they are loaded in a borehole, because of their convex ends. Accordingly, even water-bearing explosives are frequently packaged using paper or polyethylene-laminated paper, recently.
In some cases, a seepage of water or gathering of water inside a borehole (hereinafter, such borehole is referred to as "watery borehole") may happen and the water can permeate into an explosive cartridge using paper alone and can results in poor blasting performance, even in partial misfiring. In order to prevent these phenomena, paper coated with a water-proof substance, such as wax, is used to package explosives but the results are usually unsatisfactory.
Therefore, polyethylene-laminated paper has come to be used popularly for packaging dynamite, powdery explosive and water-bearing explosive. Especially a paper polyethylene-laminated on both the sides, namely paper laminated with polyethylene (hereinafter referred to as "PE") layer on both sides is preferably used since an explosive cartridge using paper PE-laminated on both the sides is best suited to load in a watery borehole.
The explosive cartridge using paper PE-laminated on both the sides has not only an advantage that it prevents water from permeating into the cartridge but also an advantage that when the explosive cartridge once loaded in a watery borehole is to be taken out for some reason and again loaded into another borehole, said cartridge is not deformed and present no problem to handle.
However, PE film has very smooth surface in comparison with ordinary paper or wax-coated paper, so that when an explosive cartridge using paper PE-laminated on both the sides is loaded into a borehole having no water, it tends to adhere closely to the flat wall of the borehole and is hard to slide, making the borehole loading operation troublesome and time-consuming. This problem is particularly remarkable when the boreholes run horizontally as in the case of tunnel boring. When the explosive cartridges are hard to slide, that is, hard to load in a borehole, a worker may often fail to effect pertinent loading of explosive cartridges by adequately pushing them into the borehole and tends to make incomplete loading only, giving rise to a possibility of forming air gaps between the cartridges, which often becomes one of causes of partial misfiring or poor blasting performance. At the site of blasting, there usually are watery boreholes and dry boreholes. It is quite unreasonable to make proper use of explosive cartridges according to whether the borehole is watery or dry. It is desirable that the explosive cartridges using water-resistant paper PE-laminated on both the sides can be applied to both types of borehole. The greatest problem in realizing this advantage, therefore, was how to make the explosive cartridge using paper PE-laminated on both the sides easy to slide, that is, easy to be loaded in a borehole no matter whether it is watery or dry.
As a result of extensive studies of the present inventors to solve the problems on the subject matter, it has been found that when an explosive cartridge is prepared using a paper PE-laminated on both the sides, in which at least one of the outer surfaces thereof has been subjected to a specific treatment so that the treated surface has an angle of slide of not more than 12 degrees, such an explosive cartridge can be loaded smoothly, with little resistance, into boreholes having no moisture nor water.